This invention relates to a power transmission device for a vehicle having a first power transmitting path with a reduction gear and a second power transmitting path with a stepless speed change gear mechanism so as to transmit power by one of the paths according to a driving condition of the vehicle.
Conventionally, there has been a known power transmission device for transmitting an engine output of a vehicle including a first power transmitting path with a reduction gear (at least one-step speed change mechanism), a second power transmitting path with a stepless speed change gear mechanism and a clutch for switching the paths (for example, lockup clutch), wherein the first and second paths are switched by connecting and disconnecting the clutch according to the driving condition of the vehicle so as to transmit the power by one of the paths (refer to Japanese Patent Application Laying Open Gazette No. 2-240444).
The power transmission device is set so as to obtain a comparatively large change gear ratio at the first path and a continuously changeable change gear ratio in a range of a comparatively small change gear ratio, and to transmit the engine output, for example, by the first path when the driving condition is in a driving range of low vehicle speed and by the second path when the driving condition is in a driving range of high vehicle speed. Thus, the appropriate change gear ratio is set and adjusted in each driving range.
Such the kind of power transmission device, however, cause a shock owing to switch-over of the paths by a clutch operation and the clutch is worn out in short period.